1. Field of the Invention
The present invention relates in general to a fuel supply apparatus for an internal combustion engine of a fuel injection type. In particular, the invention concerns a fuel supply apparatus in which intake air quantity is detected by an air valve disposed within an intake conduit upstream of a throttle valve and adapted to be so controlled that pressure in an air pressure chamber defined between the air valve and the throttle valve may be maintained constant, while fuel quantity to be supplied to the internal combustion engine is controlled by a fuel metering assembly operationally interlocked with the air valve so as to be proportional to the intake air quantity.
2. Description of the Prior Art
The fuel supply apparatus of the above type permits a predetermined air-fuel ratio of air-fuel mixture to be established with a relatively high accuracy during normal operation of internal combustion engines, whereby purification of exhaust gas from the engine can be accomplished to a reasonable degree. However, in order to attain an adequate and satisfactory purification of the exhaust gas under all various operating conditions of the engine, it is necessary to perform correction on the air-fuel ratio in consideration of the instantaneous operating and environmental conditions such as temperature of ambient air, atmospheric pressure, temperature of the engine, acceleration and deceleration of the engine and the like.
From Japanese Laid-Open patent application No. 38220/73, which corresponds to U.S. Pat. No. 3,809,036, a fuel supply apparatus of the aforementioned type has been already known in which the ratio of the metered fuel quantity relative to the intake air quantity is caused to vary by correspondingly varying a fuel pressure difference produced across the fuel metering device in dependence on a certain specified operating condition of the engine, thereby to permit the air-fuel ratio to be corrected to obtain the optimum ratio. However, this known apparatus is disadvantageous in that the structure is complicated, the air-fuel ratio is corrected merely in response to change of only one factor representing a specified operating condition of the engine, and a fine control of the air-fuel ratio can not be accomplished in a satisfactory manner due to the fact that the apparatus is operated on the basis of proportional control principle and thus exhibits unstable follow-up performance in response to abrupt changes in the intake air quantity.